1. Field of the Invention
The present invention relates to a data decoding apparatus and method, and a storage medium and, more particularly, to decoding processing of decoding a bitstream such as coded and multiplexed image and audio signals in a digital TV reception apparatus or a digital storage medium reproduction apparatus.
2. Related Background Art
FIG. 1 shows a conventional decoding apparatus for decoding a coded bitstream. FIG. 1 shows the arrangement of a digital broadcasting receiver that has an accounting function. Referring to FIG. 1, the apparatus comprises a bitstream input terminal 101 for receiving a coded bitstream, descrambling circuit 102, and separation circuit 103 for separating multiplexed data.
The apparatus also has an audio signal decoding circuit 104 for decoding a separated audio signal, a video signal decoding circuit 105 for decoding a separated video signal, a CPU 106, an IC card 107, and a remote controller 108. The operation of the conventional digital broadcasting receiver will be described below with reference to FIG. 1.
A bitstream received by a tuner (not shown) in FIG. 1 is input from the input terminal 101 to the apparatus. As the coding scheme, so-called MPEG (Moving Picture Experts Group) 2 is used.
In this input stream, normally, a coded audio signal and video signal are multiplexed and scrambled to permit only a specific user to view the contents.
A method of confirming viewing permission will be described later. If viewing is permitted, the stream input to the descrambling circuit 102 is descrambled by a descrambling key given by the CPU 106 and input to the separation circuit 103.
The separation circuit 103 separates the stream into an audio signal stream and a video signal stream, which are supplied to the decoding circuits 104 and 105, respectively, decoded, and displayed on a monitor (not shown). Control lines from the CPU 106 are connected to the audio signal decoding circuit 104 and video signal decoding circuit 105 to control stereo/multi-lingual data or display information on the screen.
A method of confirming viewing permission (authentication method) will be described.
A subscribed program ID and descrambling key are stored in the IC card 107 in advance. To watch the program, the CPU 106 accesses the IC card 107 and confirms viewing permission on the basis of whether the program ID stored in the IC card and the program of the input stream coincide with each other. In this case, programs that are not subscribed in advance cannot be watched.
Conventionally, however, in any schemes, viewing is limited in units of channels or in units of programs. In addition, only ON/OFF-control can be performed. For this reason, it is difficult to provide higher-quality video data in accordance with subscription or provide an interactive program.
In recent years, large-capacity media such as DVD are becoming popular, and not only fixed control for reproduction/non-reproduction but also a variety of flexible use forms that take advantage of the large capacity are required. However, such a service is hard to realize.